Green tea: Does it really do anything?

Green tea and its presumed active ingredients, the polyphenols epigallocatechin, epigallocatechin gallate, and others (“green tea catechins”), are among the most studied components of food with presumptive health benefits. There are many varieties of green tea, of course, such as the Japanese sencha, macha, and kukicha and the Chinese chun mee, lung ching, mao feng and many others that all vary in composition. In general, green tea catechins comprise approximately 30% of the dry weight of tea. Compared to white, black, and oolong teas, green tea contains the greatest polyphenol catechin content. One cup of brewed green tea typically contains 50-100 mg of green tea catechins.

Health benefits that appear to be associated with increased consumption of green tea catechins include:

• Cancer prevention—Abundant experimental evidence suggests that the green tea catechins block several steps in cancer development.
• Weight loss–Daily intake of green tea catechins, 270 mg to 1200 mg/day, has modest weight-reducing effects.
• Blood pressure reduction–Although the effect is modest (typically no more than 2 mm Hg reduction in systolic pressure), green tea catechins reduce blood pressure.
• Anti-inflammatory effects—Mediators of inflammation are reduced by green tea catechins. Anti-inflammatory IL-10 is increased (an effect shared, by the way, with L. reuteri and the oxytocin boost it generates). It may be the anti-inflammatory effects that underlie reductions in risk for cancer, heart disease, blood pressure, etc.
• Depression—Preliminary evidence suggests that green tea may reduce risk for depression.

A pretty impressive list.

Like most other polyphenols, green tea catechins are not well absorbed. There have been a number of efforts aimed at increasing absorption to potentially improve health benefits. But, as I have speculated with the very poor absorption of curcumin, could at least some of the benefits of green tea work via effects on bowel flora or the intestinal mucus barrier? The above list of potential benefits of green tea catechins looks virtually identical to the list of benefits of reversing small intestinal bacterial overgrowth, SIBO, and/or reducing endotoxemia.

Green tea catechins have been shown to be effective antimicrobials against Streptococcus mutans that causes dental decay; E. coli, Salmonella, Enterococcus, Pseudomonas, and Staphylococcus–species that characterize dysbiosis and SIBO, as well as several fungi including Candida albicans. Green tea catechins may also increase selected species of Lactobacillus, Bifidobacteria, and Clostridia. There may be a modest boost to Akkermansia, also. In other words, green tea catechins may essentially shape the intestinal microbiome by encouraging proliferation of probiotic species, while suppressing undesirable, potentially pathogenic, species.

Green tea catechins also generate mucin cross-linking, i.e., proteins within intestinal mucus are cross-linked by green tea catechins, converting semi-liquid intestinal mucus barrier to a gel, increasing its protective ability and reducing penetrability to such things as bacterial lipopolysaccharide, the primary driver of endotoxemia.

In other words, green tea may exert much, perhaps most, of its benefits via the microbiome, the intestinal barrier, and reduced endotoxemia. Add green tea to the list of foods advantageous to your microbiome and overall health but for different reasons than generally discussed.